Abstract: Objectives The purpose is to address the low-frequency limitations in the computation of hydrodynamics for slender ships using the strip theory, and to develop an efficient method for calculating hydrodynamics over a wider frequency range for slender ships using a simplified approach. Methods Based on the unified theory combining the strip theory and the general slender body theory, the added mass and damping coefficients of a prolate spheroid, slender modified Wigley model, and S60 ship were calculated programmatically. A comparison was made between the calculated results using the unified theory and the experimental data, as well as results obtained from the strip theory, 3D translating and pulsating source Green’s function method and other methods. The computational characteristics and advantages of the unified theory were analyzed. Results The results indicate that the unified theory based on the 2D sections produces results for zero-speed conditions that are consistent with those obtained from the 3D panel method. For conditions involving ship speed, the calculated results exhibit consistent variations with those obtained from the 3D translating and pulsating source Green’s function method. Conclusions The unified theory is capable of reflecting the 3D effects in the low-frequency region, exhibiting greater efficiency and simplicity compared to 3D methods, thus possessing significant practical value.